Cellular material and blowing agent therefor



Patented Oct. 7 1952 CELLULAR MATERIAL AND BLOWING AGENT THEREFOR DonaldV. Sarbach, Cuyahoga Falls, Ohio, as-

signor to The B. F. Goodrich Company, New York, N. Y., a corporation ofNew York No Drawing. Application September 2, 1950, Serial No. 183,100

19 Claims.

This invention relates to a cellular material such as a cellular rubbercomposition and pertains more specifically to a blowing agent and amethod of using the same in the manufacture of vulcanized sponge rubber.

The object of this invention is to provide a blowing agent which is moreeffective than those hitherto known and which produces a product havingsuperior properties.

Another object is to provide a method of making a cellular material froma plastic composition which material is characterized by having a softtexture and by having cells of uniform size which are for the most partinterconnected.

Two general types of synthetic cellular material are well known, one inwhich the individual cells are discrete chambers separated from eachother by a wall of material, the other in which the individual cellsareinterconnected to provide a product which is pervious to fluids. Inmaking products of the latter type, two general methods have beenemployed, the first of which involves beating or whipping air into aliquid dispersion or solution of the binder material to form a froth orfoam, then gelling or setting the foam; the second involves dispersingin the solid binder material an ingredient which will liberate gas uponheating to form bubbles or cells. In this latter method, finely-dividedsodium bicarbonate has been one of the principal blowing agents employedup until the present time. This ingredient reacts to liberate carbondioxide upon subsequent heating of the composition. If desired, acidicmaterials may be present, such as the cottonseed fatty acids commonlyemployed in rubber compounding in order to accelerate liberation of thegas.

However, the results obtainable with sodium bicarbonate have not beenentirely satisfactory in that even by using a large proportion of thisingredient it has been impossible to reduce the apparent density of thefinished product to the desired point. Furthermore, the cells in thefinished product are larger than is desired for many purposes and arenot uniform in size but vary over a wide range. Consequently theproducts tend to be stiff and boa-rdy and of varying compressibility. Y

I have now discovered that by adding to sodium bicarbonate a smallamount of an amide having the formula (CH2N2): where a: is a smallinteger, these disadvantages are overcome and a highly desirable productis obtained. This result apparently is due to a synergistic effect between these two ingredients since the amide by itself produces only asmall degree of blow, much less than that of an equal amount of sodiumbicarbonate. The amides which I have found to be particularly effectiveare cyanamide, dicyandiamide and melamine, of which melamine ispreferred because of the superior results which it produces. A mixtureof sodium bicarbonate and amide containing from 2 to 30% by weight ofamide is satisfactory although from 3 to 10% is preferred, the bestresults being obtained by the use of about 5% of amide by weight of the.mixture.

It has been found desirable and convenient to mix the sodium bicarbonateand amide in finely-divided form prior to incorporating the mixture inthe material to be blown. However, if desired, the two ingredients maybe separately dispersed in the material to be blown. The preciseparticle size of the bicarbonate and of the amide is not critical. Ihave found commercial baking soda to be quite satisfactory, and theparticle size of the amide is preferably of the same order of magnitudeas that of the bicarbonate. Material which will pass a No. 50 U. S.Standard sieve is satisfactory, although it is preferred to use materialwhich is fine enough to pass a No. U. S. Standard sieve.

The amount of this new blowing agent which should be used will vary, ofcourse, depending upon the plasticity of the uncured composition and theapparent density desired in the finished product. Satisfactory resultshave been obtained by using from 2 to 30% of the blowing agent by weightof the binder material such as rubber. However, it is preferred in mostcases to employ from 3 to 10% by weight.

My new blowing agent may be used with any heat-softening orthermoplastic binder material which is capable of being blown to acellular product by means of sodium bicarbonate alone. regardless ofwhether the material is hardened or set in its cellular condition merelyby cooling or by a chemical reaction such as vulcanization. Among suchbinder materials are phenol aldehyde resins, urea formaldehyde resins,melamine formaldehyde resins, polyethylene, polyisobutylene, polyvinylresins such as polyvinyl acetals, plasticized polyvinyl chloride,various copolymers of vinyl chloride with other polymerizable materials,and natural or synthetic rubbers such as caoutchouc (a polymer ofisoprene) and various other rubbery conjugated diene polymers such asthe rubbery polymers of butadiene-1,3, chloroprene, 2,3-dimethylbutadicne and the like and rubbery copolymers of these materials witheach ,189 I v: m

alone as a blowing agent, it is desirable but not.v

essential that some acidic ingredient bepresent in the composition toreact with the sodiun'i'bicarbonate upon heating to liberate a gas andcause cell formation. Preferably'thisacidic ingredient is an organicacid such asthe iatty acids commonly employed in rubber compounding.

The following specific examples are intended as illustrations of myinvention but not as 9. 'mmcation thereon.

Example 1 .LThe following, composition was prepared by mixing. theingredients on a roll mill, thesodium bicarbonate being added last:

rans by weight Crude rubber 100.0

Whiting -85.0 Channel black -2.'0 Zinc oxide 15.0 Sulfur i a MiheraLoil10.0 Cottonseed fatty acid 20.0 fiei ola m 2- Sincere. wax 2.0Accelert'or benzothia yl' disul de) 0.6 Sodium bicarbonate (commercialbaking soda) 20.0

Total 2491s The composition was heatedin a mold at 300 F.v for 30minutes to cause cellformation and vulcanization. By usingvariousamounts of this rubbercomposition it was determined that 100gramsofthecomposition was required to produce a cellular productcompletely filling a standard mold (18 cu. in.), the product havingan-apparent density of .22 oz. per cu. in, When less than 100. g. of thecomposition was employed/the material failed to fill out the moldcompletely during the blowing stage.

.The.,.product in this case was stiff and boardy and the individualcells varied consideraly in size from about to about in diameter. Thisnon-uniformity in size of, the cells resulted in. the product havingvarying compressibility at different spots, one area being quite firmwhile another adjacent area was relatively soft.

Example 2 :per.cu.,in. The product was characterized by a soft textureand very'uniiorm cell size, (about 3 :1), which was considerably smallerthan the cell size of the product prepared using sodium b1- carbonatealone.

' Example 3 i The sodium bicarbonate of Example 1 was re-- placed withparts by weight of a mixture of "IO parts by weight of sodiumbicarbonate with 30 parts by weight of melamine. The results obtainedwere similar to those of Example 2.

Example 4 :'I hesodium bicarbonate of Exampleiljwas replaced with 5parts by weight of a mixture of 95 ;parts by weight of sodiumbicarbonate and 5 parts of cyanamide and treated as in Example 1..Inthis case it was found that the 5 parts of new blowing -agent wasapproximately equivalent in blowing power to, 2 0 parts of sodiumbicarbonate,

about 100g. of the composition being required to fill thestandard mold.In addition, the product was similar to that of Examples 2 and 3 in texture'and'uniformity of cell size.

Example 5 The sodium bicarbonate of Example 1 was replaced with 5 partsby weight of amixtureof 95 parts by weight'of sodiurn'bicarbonate' with5 parts vofdicyandiamide'and treated as in Examplel.,.. p

The results in this casewere appr ximates the same as those obtained inExample 4.

Exampleo The sodium biaiboaaeiqf.E ample}; was re-,-

placed with 10 parts by weightlof amiXturei fQS parts by weight ofsodium bicarbonatefwithfl parts; of melamineand treated-as in nxam leigTheresults. were similar tothose in Exampleb.

"Similar results were obtained using as; little" as, 2 partsbyweight'of'the newblowmgagefit other binder materials such asv phenolicresins,-

polyvinyl resins or the like, the various minor changes in the otheringredients usually present in the. compositionwill be .apparentftothose skilled in the art. VulcaniZable syntheticrubberssuohasbutadiene-styrene copolymers, butadiene-isobutylene copolynie'rs,r'ieoprerie, and the'like, may be used in, place of the crude rubberinthe recipe given in Example 1 of course, with only theconventionalchanges in amount and kind of vulcanizing agent,accelerator, plas ticizer, etc, as are well knowntotheart Obviousvariations and modifications which are within the scope of the appendedclaims will be apparent to those. skilled in the art.

1. A blowing agentcomprisingamixture of solid, -finely divided sodiumbicarbonate with from 2 to 30%, by weight'of the mixture, ofa solid,finely-divided amide selected from the class consisting of cyanamide,dicyandiamide, and

v melamine.

. mixture, of finely-divided cyanamide.

, sisting of cyan'amide, dicyandiamide, and mela- 3. A.blowing agentcomprising solid, finelydivided sodium bicarbonate. having imiiormlymixed therewith from 3 to 10%, by weight of the 4. A blowing agentcomprising solid, finelydivided sodium bicarbonate having uniformlymixed therewith from 3 to by weight of the mixture, of finely-divideddicyandiamide.

5. A blowing agent comprising solid, finelydivided sodium bicarbonatehaving uniformly mixed therewith from 3 to 10%, by weight or themixture, of finely-divided melamine.

6. A composition capable of being blown to cellular form comprising aheat-softening binding material having dispersed therein a mixture infinely-divided form, of sodium bicarbonate with from 2 to by weight ofthe mixture, of an amide selected from the class consisting ofcyanamide, dicyandiamide, and melamine.

7. A composition for making cellular material which comprises avulcanizable rubbery diene polymer having dispersed therein aparticulate mixture comprising sodium bicarbonate and from 3 to 10%, byweight of the mixture, of an amide selected from the class consisting ofcyanamide,

dicyandiamide, and melamine.

8. A composition for making cellular material comprising a vulcanizablerubber containing dispersed therein from 2 to 30%, by weight of therubber, of sodium bicarbonate and an amide selected from the classconsisting of cyanamide, dicyandiamide, and melamine, said amideamounting to 2 to 30% of the total weight of said bicarbonate and amide.

9. A composition for making cellular material comprising a vulcanizablerubber containing dispersed therein from 2 to 30%, by weight of therubber, of sodium bicarbonate and cyanamide, said amide amounting to 3to 10% of the total weight of said bicarbonate and amide.

10. A composition for making cellular material comprising a vulcanizablerubber containing dispersed therein from 2 to 30%, by weight of therubber, of sodium bicarbonate and dicyandiamide, said amide amounting to3 to 10% of the total weight of said bicarbonate and amide.

11. A composition for making cellular material comprising a vulcanizablerubber containing dispersed therein from 2 to 30%, by weight of therubber, of sodium bicarbonate and melamine, said melamine amounting to 3to 10% of the total weight of said bicarbonate and melamine.

12. The method of making a spongy material which comprises dispersing ina heat-softening composition finely-divided sodium bicarbonate and anamide selected from the class consisting of cyanamide, dicyandiamide,and melamine, said amide amounting to 2 to 30% of the total weight ofsaid bicarbonate and amide, and heating said composition to soften itand to liberate gas from said bicarbonate to form interconnected cellsof uniform size dispersed throughout said composition.

13. The method of making a cellular sponge composition which comprisesdispersing in a composition comprising a vulcanizable rubbery conjugated diene polymer from 2 to 30%, by weight of said polymer, ofsodium bicarbonate and cyanamide, said amide amounting to 3 to 10% ofthe total weight of said bicarbonate and amide, and heating saidcomposition to soften it and to liberate gas from said bicarbonate toform interconnected cells of uniform size dispersed throughout saidcomposition and to vulcanize said composition.

14. The method of making a cellular sponge composition which comprisesdispersing in a composition comprising a vulcanizable rubbery conjugateddiene polymer from 2 to 30%, by weight of said polymer, of sodiumbicarbonate and dicyandiamide, said amide amounting to 3 to 10% of thetotal weight of said bicarbonate and amide, and "heating saidcomposition to soften it and to liberate gas from said bicarbonate toform interconnected cells of uniform size dispersed throughout saidcomposition and to vulcanize said composition.

15. The method of making a cellular sponge composition which comprisesdispersing in a composition comprising a vulcanizable rubbery conjugateddiene polymer from 2 to 30%, by weight of said polymer, of sodiumbicarbonate and melamine, said melamine amounting to 3 to 10% of thetotal weight of said bicarbonate and melamine, and heating saidcomposition to soften it and to liberate gas from said bicarbonate toform interconnected cells of uniform size dispersed throughout saidcomposition and to vulcanize said composition.

16. The method of making a cellular sponge composition which comprisesdispersing in a composition comprising a vulcanizable rubbery conjugateddiene polymer from 3 to 10%, by weight of said polymer, of sodiumbicarbonate and melamine, said melamine amounting to about 5% of thetotal weight of said bicarbonate and. melamine, and heating saidcomposition to soften it and to liberate gas from said bicarbonate toform interconnected cells of uniform size dispersed throughout saidcomposition and to vulcanize said composition.

17. A composition for making cellular material which comprises aheat-softening binding material having dispersed therein a mixture infinelydivided form of sodium bicarbonate with from 2 to 30%, by weightof the mixture, of melamine.

18. A composition for making cellular material which comprises aheat-softening binding material having dispersed therein from 3 to 10%,by weight of said binding material, of a mixture in finely-divided formof sodium bicarbonate with from 3 to 10%, by weight of the mixture, ofmela mine.

19. The method of making a spongy material which comprises dispersing ina heat-softening composition finely-divided sodium bicarbonate andmelamine, said melamine amounting to to 10% of the total weight of saidbicarbonate and melamine, and heating said composition to soften it andto liberate gas from said bicarbonate to form interconnected cells ofuniform size dispersed throughout said composition.

DONALD V. SARI-EACH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,341,180 Jayne Feb. 8, 1944.2,544,483 Baum Mar. 6, 1951 OTHER REFERENCES Schwarz India Rubber World,May 1946, pages 211 and 212.

6. A COMPOSITION CAPABLE OF BEING BLOWN TO CELLULAR FORM COMPRISING A HEAT-SOFTENING BINDING MATERIAL HAVING DISPERSED THEREIN A MIXTURE IN FINELY-DIVIDED FORM, OF SODIUM BICARBONATE WITH FROM 2 TO 30%, BY WEIGHT OF THE MIXTURE, OF AN AMIDE SELECTED FROM THE CLASS CONSISTING OF CYANAMIDE, DICYANDIAMIDE, AND MELAMINE. 